When attaching (welding, brazing, gluing, etc.) a seatstay and/or chainstay to a bicycle dropout, it is common to make one dropout for every frame size (seven average frame sizes and there can be special frame sizes). This is done to optimize weight, aesthetic appearance between seatstay and chainstay and dropout and manufacturability of each frame. Having many different dropouts is very costly since each dropout requires starting forms, forging dies and trim dies, as well as smaller production runs and more parts to inventory. A typical fixed design is shown in FIG. 3: the lower ends of the seatstay tube ST is snugly telescoped over annular stud projections P. The concept of adjustable dropouts has been around for many years. One such design is shown in Muller et al U.S. Pat. No. 4,813,591 from which FIGS. 1 and 2 hereof are taken. In this design, a ball element BE is formed on the dropout DO and a socket portion is shaped on the lower butt end L of the seize ST so that in effect a ball and socket universally adjustable joint is formed which can be welded in place at the desired angle for a given frame size. A similar arrangement is provided for the connecting the chainstay tube to the dropout.
This design reduces the contact area between tube end and dropout resulting in approximately 80 degree of entrapment, limiting the manufacturer to using the outside surface of the domed ends of the tube or the ends of the tube. This makes the fit-up for the assembler difficult to maintain accurate placement for fast high volume and high accuracy placement. Under normal doming operations the end surface is rough due to the swaging or pointing operation because the metal is being gathered and work hardened with some grain structure gathering more rapidly than others. When locating off of the end of the domed tube end, additional machining or forming operations may be required for truly accurate locating. In FIG. 15 of Mueller et al, it is clear that the side rotation of the tube drastically reduces the entrapment region and provides little side-to-side stability. On FIG. 10, there is approximately 80.degree. of entrapment, again using only the end of the seatstay for location.
The object of the present invention is to provide an improved bicycle dropout system and, more particularly, an improved adjustable dropout which can accurately accommodate a wide variety bicycle frame sizes.
According to the present invention, a locating edge is formed in the lower end of the seatstay tube and a mating locating pin on a seatstay projection on the dropout. This will allow the seatstay tube to rotate fore and aft freely on the outside of the locating pin. The pin should be placed at a perpendicular angle to the centerline of the tube. The pin could be attached to the welding fixture rather than the dropout, providing essentially the same function while eliminating the pin on the dropout. This will assure accurate locating or positioning of the parts relative to each other thereby allowing for accurate and rapid positioning of the parts.
The locator pin does not necessarily need to be round. Since its purpose is to help locate the centerline of the part, the locator could actually be a triangular protrusion having one of the corners acting as the contact point. The purpose of this pin is to serve as a stop to keep the tube from slipping over center of the radius profile of the dropout, and thus does not need to be precisely in the center. If the locator pin is within proximity of the center, it will suffice due to the tolerances required and the ability of the assembler to maneuver the part into place. When using a formed tube, such as a rectangular tube, the pin serves as a stop as opposed to a locator. The actual location of the tube is carried out by the internal rectangular mating surfaces which will dictate the orientation of the tube. The pin will allow the tube to rotate only about the axis centered on the pin. On spherical ball style dropouts, there is no formed shape to control the tube placement, therefore a notch can be utilized to help speed up the assembler and accurately control for any unwanted rotation.
In a preferred embodiment, the dropout member has an integral rectangularly formed stay tube projection which provides approximately 170.degree. of engagement on straight ID walls providing a positive fit on all sides. In a further embodiment the seat tube projection is generally spherically shaped and a pivot pin notch is formed in the lower edge of the seatstay tube, the entrapment of seatstay ID is approximately 170.degree.. Moreover the present invention restricts unwanted rotation by allowing only fore an aft rotation about a centerline defined by the pin on the outside profile of a spherically shaped portion. When using pre-mitered, or pre-formed seatstays, locating of the part is critical to fit-up. (In this context the prior art discussed above require further fixturing in order to ensure a proper fit between the seatstays and the seat tube; and some seatstays require additional bending for tire clearance along with the pre-metered seize for fit-up between seize and seat tube thereby adding to the location problem.)
The present invention will locate the end of the seatstay tube using the internal diameter (ID) of the tube (straight or formed) to the dropout's outer surface or ball using a pin to prevent the seat stay from slipping over center. By notching the end of a straight (not formed) seatstay, the pin will act as a positive locator for the tube ensuring an accurate fit-up with the seat tube. This is not accomplished by the prior art. The dropout of the present invention can have approximately 170.degree. of engagement which inherently provides a much more stable interface. The invention can accommodate brazing, welding or gluing.